In current spontaneous ignition internal combustion engines (i.e. operating according to the “Diesel” cycle and fed with oil fuel or the like), a low-pressure pump feeds the fuel from a tank to a high-pressure pump, which in turn feeds the fuel to a common rail. The common rail is adapted to contain the pressurized fuel for feeding the fuel itself to the injectors (one for each cylinder of the engine), which are cyclically driven to inject part of the pressurized fuel present in the common rail into the corresponding cylinders. For the correct operation of the combustion, it is important for the fuel pressure value within the common rail to be constantly maintained equal to a desired value, which is generally variable as a function of the engine point and in modern engines is very high (even higher than 2000 bars). In order to work at such high pressure values, in this type of internal combustion engine, the common rails are very heavy components formed by forged steel.
In current systems, the common rail is directly fastened either to the crankcase or to the engine head, i.e. at the metallic parts of the engine by means of fastening screws; alternatively, the common rail may be fastened directly to the intake manifold formed by aluminium by means of the fastening screws. If the intake manifold is formed by thermoplastic material, the common rail must necessarily be fastened either to the crankcase or to the engine head because the intake manifold is not sufficiently rigid to support the common rail and withstand the vibrations which are caused by the engine and by the tensions which are induced by the delivery pipes which connect the common rail to the injectors and by the feeding tubes which connect the common rail to the high pressure pump.
However, fastening the common rail either to the crankcase or to the engine head has some drawbacks, as it forces to use longer and more complexly shaped delivery pipes which connect the common rail to the injectors with a consequent increase of manufacturing costs, assembly costs and load losses.